Fidget spinning the eclipse

What do fidget spinners, the latest fad toy and new student favorite, have to do with the upcoming solar eclipse? Teachers don’t despair, fidget spinners can demonstrate physics concepts and orbital mechanics for kinesthetic learners. The eclipse is all about gravity, and the rotation of celestial bodies. As the fidget spinner spins about its central axis, an object on the arm of the spinner (or two or three) is locked in rotation around the central object. Much like the Earth rotates around the Sun. So for that, picture a solar fidget spinner 93 million miles from the center to the edge!

We are on a giant fidget spinner, rotating once per year, smoothly going around the Sun for billions of years in the “ecliptic” fidget spinner plane. Sped up for galactic time, it looks just like this:

Now zoom in on the Earth. It has its own fidget spinner, the Moon which rotates around the Earth! The arm of that extraterrestrial fidget spinner is “only” 250,000 miles. The Moon rotates once every 27 days for 4.5 billion years (just a little younger than the Earth). And here’s the key to understanding eclipses, the lunar fidget spinner is tilted like so, 5° out of the ecliptic Sun-Earth plane.

So try to picture these two huge fidget spinners with different periods, size, and tilt. When they line up a total solar eclipse can be caused! They intersect only rarely but there is a pattern to some of those intersections. It’s 18 yrs ten and one third days. More about that pattern here (Saros cycle) and in the next post.

Finally, there’s one more similarity between your average fidget spinner and celestial orbital mechanics. Gravitationally driven celestial fidget spinners go for cosmically long times, but they also have tiny deviations and wobbles, just like your fidget spinner might (look at it edge on, and you may notice some small wiggles). The Earth and the Moon are not perfect spheres, and their orbits are not perfect circles. So there’s a little bit of variation in their spinning, due to minute manufacturing differences, just like that spinner you got from 7-11. 😉 The moon usually looks like a perfect circle, but during a solar eclipse, some of the features you see like Bailey’s Beads and the “diamond ring” effect are actually due to its not being a perfect sphere, but being heavily cratered.

Activity ideas:

Close your eyes and picture a huge solar fidget spinner.

Draw it. Spin it. Label the Sun and the Earth,

Close your eyes and picture the smaller lunar fidget spinner going around the Earth.

Draw it. Spin it. Be sure to have the tilt.

Now put those two drawings together to illustrate the eclipse.

Last, look at your fidget spinner edge on. Do you see the way it isn’t perfect?